Narrow Results

We provide a review on the status of theoretical modeling of tautomerization in free-base porphyrin. We focus our discussion on several aspects, namely: (1) potential surfaces for both the stepwise and concerted mechanisms calculated at different levels of theory, (2) solvent effects and (3) kinetics. The importance of quantum mechanical tunneling in this double hydrogen atoms transfer process is analyzed.

The influence of anodized film on corrosion and electrochemical behavior of extruded magnesium alloy AZ63, cast and die-cast magnesium alloys AZ91D were investigated by using immersion technique, electrochemical methods, SEM, EDAX, IR and XRD. The results showed anodized film could improve remarkably corrosion resistance. Protection effect was different with the same anodizing process because formation status of anodized film of different materials was different. The formation status of anodized film was related to alloy microstructure as revealed by optical and scanning electron microscopy. The formatting process and casting method strongly influences the corrosion performance by affecting on the alloy microstructure. A tentative corrosion mechanism is presented explaining the corrosion behavior of anodized magnesium alloy.

The McMurry crossed coupling reactions of p,p′-disubstituted benzophenones (1) with pivalaldehyde (Pv) gave the corresponding ethenes (2) in fair to excellent yield. The observed geometrical selectivity is varied depending on a kind of p-substituent of the aromatic moiety of 1, when p′-substituent is limited to methyl. According to the known reaction mechanism, the reason why the geometry selection occurred is discussed by a conformational analysis of a possible intermediate, titanium bound pinacolate, and molecular orbital calculations of the starting carbonyl compounds. As a result, the selection is caused by electronic and stereochemical structures of anion radical of 1 and approaching mode of Pv anion radical to them. Distribution of a spin density and unsymmetrical nature of two aromatic moieties of anion radical of 1 provide predetermined pathway to bring about the pinacolate without any rotational conversion under the reaction conditions. Subsequent workup affords 2 with the observed geometry.

The charge-transfer reaction of tetraarylbutatriene 1 with tetracyanoethene (TCNE) in dichloromethane at room temperature was studied and we found a novel addition reaction. A red crystalline material 2 was isolated as an intermediate product which is converted slowly into dihydronaphthalene derivative 3 in dichloromethane but rapidly in protic solvent. The structure of the compounds was determined by X-ray crystallography. The detailed structure and the plausible reaction mechanism have also been discussed.

Nanocrystalline Cu particles were prepared by mechanochemical reduction of cuprite (CU₂O) with graphite in a high-energy ball mill. In order to gain an understanding into the possible mechanisms, the kinetic of the process was investigated using Johnson-Mehl-Avrami (JMA) model. It can be seen that theoretical calculation agrees well with experimental data. It was found that the most important effect of mechanical activation is the formation of the lattice defects and grain boundaries in addition to activated fresh surface areas during milling, which promote the reduction process. The Cu nanopowder was characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD and TEM results showed the nano-structure nature of the product processed under the synthesis conditions; the crystallite size was measured almost 30 nm in the 30 h milled powders.

This paper explores the mechanism design of a balloon machine representing a vending machine where consumers can select their desired shapes, as well as avoid bursting caused by manual inflation. Inside the machine, balloons are placed on the mechanism designed based on a waterwheel which rotates at a constant speed generated by motion among different sizes of gears. When rotating to the corresponding shaped balloon, the inflator will move under the opening to pull it out from the display point and start to inflate the balloon for the set number of seconds. After the inflation is completed, the glass door will open and the customer can take out their balloon. The main purpose of our development and design of the balloon machine is to improve the general balloon blowing and it is easy to prevent over-exposure and blast. The balloon machine can automatically inflate and detect the blowing time to improve the shortcomings of the balloon’s blast. In this way, it can effectively decrease sudden explosions and the number of frightened people.

Pedestrian-car interweaving is a prominent problem in old residential communities in Chinese cities. To achieve a better pedestrian-car separation to create a safe and comfortable living environment in old residential communities, this paper investigated the mechanism of the flows of pedestrians and cars on a road network inside an old residential community. A method for calculating the flows of pedestrians and cars was proposed to identify the road segments or nodes where the pedestrian flows are interlaced or intersected with the vehicle flows. This method was applied to the estimation of the traffic in the Wangyuehu Community of Changsha City, China. The estimated distribution of community network traffic and pedestrian-car interweaving sites was consistent with the actual situation.

In this paper, the influences of magnetic field on electromagnetic properties of water are experimentally investigated. The results clearly show that the magnetic field reduces the dielectric constant and resistance of water and increases its electric conductivity. In this study, we also find that the electric conductivity of magnetized water increases with increasing the frequency of externally applied electromagnetic field and magnetized time, but its dielectric constant and resistance are decreased with increasing the frequency of electromagnetic field and magnetized time of water. Then we can affirm that the magnetic field changes the electric properties of water. Finally, we discuss the mechanism of variation of electromagnetic properties in water, which are due to the changes of nature of charged ions and velocity of hydrogen ions as well as the changes of polarized features or dipole moments of free molecules and clusters including linear and ring hydrogen-bond chains of molecules in water under the influences of electromagnetic fields. Therefore, this study has important significance in science and can expand the applications of magnetized water in biomedicine and industry.

The enhanced photocatalytic activity of tungsten trioxide (WO₃) has been observed experimentally via doping with S element as different dopant types. Herein, a comparative study on the effect of different types of S dopant and native vacancy defects on the electronic structure and optical properties of WO₃ is presented by using hybrid Heyd–Scuseria–Ernzerhof 2006 (HSE06) density functional methods. Six possible models (S${}_{\mathrm{\text{O}}}$–WO₃, S${}_{\mathrm{\text{W}}}$–WO₃, V${}_{\mathrm{\text{O}}}$–WO₃, V${}_{\mathrm{\text{W}}}$–WO₃, S${}_{\mathrm{\text{O}}}$ + V${}_{\mathrm{\text{W}}}$–WO₃ and S${}_{\mathrm{\text{W}}}$ + V${}_{\mathrm{\text{O}}}$–WO₃) based on WO₃ are tentatively put forward. It is found that cationic S doping (the substitution of W by S) is more favorable than anionic S doping (replacing O with S), and both cases become easier to form as native vacancy defect is accompanied. The electronic structures of doped WO₃ depend on the type of dopant: anionic S doping results into three isolated levels in the upper part of valence band, while cationic S doping only induces an effective band gap reduction, which is critical for efficient light-to-current conversion. Interestingly, the isolated states near gap of WO₃ would appear as long as native vacancy defects exist. The introduced levels or reduced band gaps make the systems responsed to the visible light, even further to a range of 400–700 nm. These findings can rationalize the available experimental results and pave the way for developing WO₃-based photocatalysts.

This paper proposes a new method that obstacles are attached to both the suction and pressure surfaces of the blades to suppress cavitation development. A centrifugal pump with a specific speed of 32 is selected as the physical model to perform the external characteristic and cavitation performance experiments. SST $k-\omega$ turbulence model and Zwart cavitation model were employed to simulate the unsteady cavitation flow in the pump. The results indicate that the numerical simulation results are in good agreement with the experimental counterparts. After the obstacles are arranged, the maximum head decrease is only 1.37%, and the relative maximum drop of efficiency is 1.12%. Obstacles have minimal impacts on the variations of head and efficiency under all flow rate conditions. The distribution of vapor volume in the centrifugal pump is significantly reduced after obstacles are arranged and the maximum fraction reduction is 53.6%. The amplitude of blade passing frequency decreases significantly. While obstacles decrease the intensity of turbulent kinetic energy near the wall in the impeller passages to effectively reduce the distribution of cavitation bubbles, and control the development of cavitation. After the obstacles are set, the strength of the vortex in the impeller passages is weakened significantly, the shedding of the vortex is suppressed, flow in the impeller becomes more stable.

TiC/TiN-reinforced composite coatings were fabricated on the substrate of Ti–6Al–4V alloy using laser remelting. X-ray diffraction (XRD) was used to identify the phases in the laser-clad composite coating; the interface characterization of the dilution zone-clad zone (IDC) and the dilution zone-heat-affected zone (IDH) was observed with a scanning electron microscope (SEM). The results show that the microstructure of a cross-section has stratification characterization, and consists of the clad zone (CZ), the dilution zone (DZ), the diffusion layer (DL) and the heat-affected zone (HAZ). The layer-by-layer microstructure results from the boundary layer phenomenon of viscous melt-fluid and diffusion. The kind of reinforced particle has an effect on the interface morphology, microstructure and flow characterization of the melt-fluid. The phase constitution in the clad zone consists of (Cr–Ni–Fe), TiC, Ni₄B₃, Ti₂Ni, Cr₂B and M₂₃C₆ for TiC+NiCrBSi coating, and (Cr–Ni–Fe), TiN, NiB, Cr₂Ti and Ti₂Ni for TiN+NiCrBSi coating. The interfaces of the IDC in the NiCrBSi-clad layer is clear and clean; those of TiC+NiCrBSi and TiN+NiCrBSi are illegible. Ti–Ni phases with acicular microstructure link dilution zone and clad zone, and two kinds of phase with acicular microstructure, are similar in composition and shape.

Porous titania coatings with Ca and P elements were synthesized by plasma electrolytic oxidation (PEO). The treatment was carried out in an electrolyte containing calcium acetate monohydrate and disodium phosphate dodecahydrate (Ca/P = 5), and 4–20 μm micropores were prepared on the coatings by applied pulse frequencies of 200–1000 Hz. The surface structure, chemical composition of the TiO₂ coatings, and time-dependent variation of electric currents were studied. The result revealed that the coating micropores, which could be controlled in size, increased with higher frequency, and the coatings mainly consisted of anatase and rutile phases with varying fractions. Based on our experiment, the formation mechanism of micropores and phases of the PEO coatings was further discussed in details.

Micro-arc oxidation coatings were fabricated on 7E04 aluminum alloy substrates by micro-arc oxidation (MAO) in the electrolytes with the graphite addition varying from 0 to 8g/L (0, 2, 4, 6, 8g/L). The effect of graphite concentration on the surface morphologies, micro-hardness, thickness, phase composition and corrosion resistance of coatings was investigated. With the graphite powder concentration increasing, the oxidation voltage decreased gradually and the thickness of coatings firstly dropped down and then went up. It is found that the size of micro-pores and sintered discs declined with increase of graphite concentration. The XRD results indicated that MAO coatings mainly consisted of $\gamma$-Al₂O₃, $\theta$-Al₂O₃, SiO₂ and a little $\alpha$-Al₂O₃. The corrosion resistance of coatings was improved with the addition of graphite powder. The study reveals that the appropriate graphite powder in the electrolytes is essential to promote the performance of the coatings.

This paper has summarized five surface strengthening methods, and these methods could to improve the surface properties of materials. The selection of mechanical parts materials has determined according to their working conditions. The work-piece in using cannot avoid defects in the material. This paper has introduced surface deformation enhancement, surface phase transformation enhancement, ion implantation technology, surface diffusion and infiltration technology, chemical transformation technology and surface coating technology. And has also included the principle of every surface technology, various technologies, parameters, strengthening characteristics, as well as strengthening effect and matters needing attention. The hardness, residual stress and corrosion resistance off mechanical parts could be improved through these surface strengthening methods. It is convenient to find the strengthening method and parameters in this paper when strengthening mechanical parts.

Ultrafine nanoparticles owing to their increased surface to volume ratio, coupled with the ability to tune their surface properties through molecular modification have made them ideal for their detection and remediation of broad range of environmental contaminants. Arsenic contamination has become a worldwide epidemic and remediation of this problem needs the development of technology with improved materials and systems with high efficiency. In the present study, we have demonstrated a simple and efficient method using surface functionalized ultrafine iron oxide nanoparticles for absolute removal of arsenic from arsenic treated water with low contact time period and low adsorbent dose. The efficiency of arsenic removal has been drastically improved by considering nanoparticles of size 10 nm and subsequent surface engineering of the nanoparticles resulting more adsorption sites being exposed to arsenic. The mechanism for adsorption was identified through electron microscopic and spectroscopic studies. The adsorption equilibrium data were well fitted to Freundlich isotherm.

The results of use of chemical kinetics receptions, approaches and methods for the study of porphyrins and their metal complexes reactivity are discussed on an example of oxidation, acid-basic, and catalytic reactions of rhodium, palladium, and rhenium complexes of porphyrin in liquid solutions. The peculiarity of the porphyrin reaction rates is analyzed in a brief context of general provisions of the chemical kinetics. The opportunity to use the quasistationarity principle at the definition of the kinetic equation of the reactions with participation of metal porphyrins is shown. The transition from the process kinetic description to consideration of its mechanism is explored.

Sorption of meso-tetrakis(4-sulfonatophenyl)porphyrin (H₂tpps) onto chitosan has been investigated in aqueous medium. Kinetic and isotherm studies were carried out by considering the effects of various parameters, such as pH, initial concentration of H₂tpps solution, and temperature. The kinetic data obtained from different batch experiments were analyzed using pseudo first-, second-order, intraparticle, and film diffusion kinetic models. The equilibrium sorption data was analyzed by using Tempkin, Langmuir and Freundlich models. The best results were achieved with the pseudo second-order kinetic, Langmuir and Freundlich isotherm models. The intraparticle diffusion and film diffusion are the rate limiting steps. The amount of sorbate adsorbed at equilibrium (q_e) increased with increasing the initial concentration of H₂tpps solution, showing maximum sorption capacity of 445.21 μmol.g^-1. The activation energy (E_a) of sorption kinetics was found to be 19.47 kJ.mol^-1. Thermodynamic parameters such as change in free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) were evaluated by applying the Van't Hoff equation. Thermodynamic activation parameters such as change in enthalpy of activation (ΔH^‡), entropy of activation (ΔS^‡), and free energy of activation (ΔG^‡) were also calculated. The thermodynamics of H₂tpps sorption onto chitosan in aqueous medium indicates its spontaneous and endothermic nature.

Structural transformations during the synthesis of mayenite (Ca₁₂Al₁₄O₃₃) were investigated. The samples were prepared by a solid–state reaction and the transformations were researched by means of XRD, Rietveld analysis, SEM, and Raman spectroscopy. The three key phases (CaAl₂O₄, Ca₃Al₂O₆, Ca₅Al₆O₁₄) were identified and their role in the mayenite formation was assigned. The optimal low temperature pathway of the mayenite synthesis involving Ca₅Al₆O₁₄ intermediate was proposed.

Unsaturated hyperbranched polyester resin (UHPR) prepared by ourselves shows best comprehensive performance in linear unsaturated polyester resin (UP-191) curing system and is considered as a kind of toughness and reinforcement additive. The effect of molecular weight and content of the UHPR on the performance of the UHPR/UP-191 hybrid materials are discussed in detail, and their performance has maximum with the increase of content and molecular weight of UHPR. The impact strength of the hybrid materials containing 10–15 wt% UHPR-2 is 1.86 kJ/m², and which almost is 1.69 times of UP-191 performance, furthermore, the tensile and flexural strength can also be enhanced about 45.71% and 23.66%, respectively. The fracture surface micrograph of hybrid materials show non micro-phase separation of the UHPR/UP-191 blends which facilitates an enhanced interaction to achieve excellent toughness and strength of the cured systems by SEM and the results also are explained by a novel situ reinforcing and toughening mechanism.

Highly proton-conducting hybrid materials (P₂W₁₇V/PEG and P₂W₁₇V/PEG/SiO₂) were prepared by heptadecatungstovanadodiphosphoric heteropoly acid with Dawson structure (P₂W₁₇V, 90 wt.%), polyethylene glycol (PEG, 10 wt.% and 5 wt.%) and silica gel (SiO₂, 0 wt.% and 5 wt.%). The products were characterized by the infrared (IR) spectrum, X-ray powder diffraction (XRD) analysis and electrochemical impedance spectrum (EIS). The result reveals that their conductivity values are 1.02 × 10^-2 and 2.58 × 10^-2S ⋅ cm^-1 at room temperature (26°C) and 75% relative humidity (RH), respectively. Their conductivities increase with higher temperature and these activation energies of proton conduction are 9.51 and 14.95 kJ⋅mol^-1, which are lower than that of pure heteropoly acid (32.23 kJ⋅mol^-1). These mechanisms of proton conduction for these two materials are Grotthuss mechanism.